The present invention relates generally to the field of micro-electromechanical-system (MEMS) devices. More particularly, the present invention relates to a MEMS mirror device having large angle out of plane motion using shaped combed finger actuators and method for fabricating the same.
A MEMS device is a mirco-sized mechanical structure having electrical circuitry fabricated using conventional integrated circuit (IC) fabrication methods. One type of MEMS device is a microscopic gimbaled mirror device. A gimbaled mirror device includes a mirror component, which is suspended off a substrate, and is able to pivot about an axis caused by electrostatic actuation. Electrostatic actuation creates an electric field that causes the mirror component to pivot. By allowing the mirror component to pivot, the mirror component is capable of having an angular range of motion in which the mirror component can redirect light beams to varying positions.
One type of electrostatic actuation for a gimbaled mirror is parallel plate actuation. Parallel plate actuation uses electrodes formed on a planar surface below a suspended mirror component. A voltage is applied to the electrodes that creates an electric field that causes the mirror component to move.
A disadvantage with parallel plate actuation for a gimbaled mirror is that the force required to move the mirror component is directly proportional to the square of the distance of the gap between the electrodes and the mirror component. As such, to obtain a large range of angular motion, the mirror component must be suspended at a large height above the electrodes, which requires a large amount of voltage to produce the necessary force for actuation. Another disadvantage with using parallel plate actuation is related to the xe2x80x9csnap downxe2x80x9d phenomenon. The snap down phenomenon occurs when a certain voltage level is applied to the electrodes that causes the mirror component to snap down to the floor of the substrate thereby limiting the working range of motion for the mirror device.
Another type of electrostatic actuator for a MEMS device is a combed finger actuator. A prior combed finger actuator uses fixed straight sidewall interdigitated fingers to move a straight sidewall moving part having a same height as the interdigitated fingers. Typically, the straight sidewall interdigitated fingers are fabricated using a simple photolithography and a single etch step. A voltage is applied to adjacent straight sidewall interdigitated fingers that produce an electrostatic force that causes the moving part to move. Although a small out-of-plane motion is possible by placing a ground plane and altering the net electric field in the out-of-plane direction, such prior combed finger actuators using straight sidewall interdigitated fingers and straight sidewall moving part provided only in-plane motion for the moving part.
A disadvantage with such a prior combed finger actuator is that it does not provide significant out-of-plane motion and therefore is not suitable for a MEMS mirror device. That is, a gimbaled mirror devices requires large motion in the out-of-plane direction to redirect beams of light.
Another prior electrostatic actuator for a MEMS device, which provides out-of-plane motion, uses straight sidewall interdigitated fingers and a straight sidewall moving part that is a smaller in height than the fixed interdigitated fingers. Thus, a voltage potential applied on the fixed interdigitated fingers creates an electric field that is asymmetric with respect to the moving part that causes the moving part to move in an out-of-plane motion. For such a prior electrostatic actuator, the farthest distance the moving part can move is at the equilibrium position specified in the Z-direction, which is approximately at a center position between the fixed interdigitated fingers.
A disadvantage with this type of actuator is that to move the moving part in the out-of-plane direction a large amount of voltage and force is required. That is, the magnitude of net electric field in the out-of-plane direction decreases significantly as the moving part moves in the out-of-plane direction. Thus, to move the moving part to the equilibrium position, a great amount of force and voltage is required.
A micro-electro-mechanical-system (MEMS) mirror device is disclosed. The MEMS mirror device includes a mirror component that is capable of moving upon electrostatic actuation. The MEMS mirror device also includes one or more electrostatic actuators providing electrostatic actuation. The electrostatic actuators having shaped plates disposed approximately perpendicular to the mirror component. The shaped plates are disposed to define a gap between the plates that decreases along a direction perpendicular to a surface of the mirror component.
An electrostatic actuator for a MEMS mirror device is disclosed. The electrostatic actuator includes two or more shaped fingers. The shaped fingers are configured to define a gap between the shaped fingers that decreases along a direction perpendicular to a top surface of the shaped fingers.
A MEMS mirror device fabrication method is disclosed using a single substrate. A pattern is formed on the substrate such that the pattern is used to define a frame pattern, electrostatic actuators, mirror component, and support structure. Portions of the substrate are removed selectively using the pattern to form the frame pattern, electrostatic actuators, mirror component, and support structure such that the electrostatic actuators define a gap that decreases along a direction perpendicular to a surface of the mirror component.
An electrostatic actuator fabrication method for a MEMS mirror device is disclosed. Two or more shaped fingers are formed from a single substrate. The shaped fingers are formed to define a gap between the fingers that decreases along a direction perpendicular to a top surface of the fingers so that a movable finger may move in an out-of-plane direction.
Other features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description, which follows below.